1. Algorithms vs. Programming
CSE Module 1
Algorithms vs. Programming
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CSE 1321 Module 1

2. Motivation
To learn algorithmic thinking with emphasis on pseudocode development; To understand what an algorithm is and how to write an algorithm; To describe the concept of abstraction To describe the relationship between algorithms and programming
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CSE 1321 Module 1

3. Topics Algorithms Fine, then what is Programming? Definition
Properties of Good Algorithms
Describing Algorithms
Examples
Components of Algorithms
Fine, then what is Programming?
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CSE 1321 Module 1

4. What is an Algorithm? What it’s not: a logarithm** What it is:
A set of logical steps to accomplish a specific task
A set of direction/instructions
You use them everyday, even right now
Algorithms contain:
Data
Instructions that work on that data
**.. Which shares the same letters as “algorithm”
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5. Algorithms: the visual
Too much screen time
Input Data
Algorithm
Output Data
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6. Chocolate Chip Cookies
Algorithms: a Recipe
Chocolate Chip Cookies
Ingredients: 2 1/4 cups flour tsp salt 1 tsp baking soda 2 eggs 3/4 cup brown sugar tsp vanilla ext. 3/4 cup granulatd sugar cup soft butter 12oz. semi-sweet chocolate chips
Instructions Preheat oven to 375°. Combine flour, salt, baking soda, in bowl, set mixture aside. Combine sugars, butter, vanilla, beat until creamy. Add eggs and beat. Add dry mixture and mix well. Stir in chocolate chips Drop mixture by teaspoons onto ungreased cookie sheet Bake 8 to 10 minutes
Where’s the:
- Input data?
- Algorithm?
- Output data?
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7. Abstraction – the level of detail
a general idea or term
an impractical idea; visionary and unrealistic
general characteristics apart from concrete realities, specific objects or actual instances
(Random House Dictionary of the English Language)
In computing:
Abstraction refers to the LOGICAL GROUPING of concepts or objects
We want to hide the details (in functions – later)
We like to think at a high level of abstraction (no details)
Too many details overwhelm us!
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8. Someone tell me to turn off the lights
Abstraction Example
Someone tell me to turn off the lights
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9. What is Wrong with this Algorithm?
(From back of shampoo bottle)
Directions:
Wet Hair
Apply a small amount of shampoo
Lather
Rinse
Repeat
Lesson learned: Just because we have algorithm
doesn’t mean it’s a good one
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10. Properties of Good Algorithms
Good algorithms are:
Precise – why?
Unambiguous – why?
Complete – why?
Correct – why?
Simple – why?
Contain levels of abstraction – why?
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11. Describing Algorithm Can be created using:
Natural language (e.g. English)
Pictures or flowcharts
Pseudocode or a specific programming language
We’ll use pseudocode in this course
It’s a mixture of languages
Not concerned with syntax, but concepts
You’ll use it through the rest of your career
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12. Example: Natural Language Algorithm
START by make a list of courses you want to register for, in order of priority.
Number of hours = 0.
Choose highest priority class on list.
IF the chosen class is not full and its class time does not conflict with classes already scheduled, THEN register for the class:
4.a. Add the class to the schedule.
4.b. Add the class hours to the number of hours scheduled.
Cross that class off of your list.
Repeat steps 3 through 5 until the number of hours scheduled is >= 15, or until all classes have been crossed.
END ALGORITHM.
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13. Example: Flowchart Algorithm
END
START
Make list of classes you want to take
Num Hours = 0
Choose highest priority class on list
Add the class to your schedule. Add class hours to Num Hours.
Cross the class off your list.
yes no
Is this class full?
Is there a time conflict?
Num Hours >= 15?
More classes on list?
Example: Flowchart Algorithm
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14. Components of Algorithm
Any computing algorithm will have AT MOST five kinds of components:
• Data structures to hold data
• Instructions to change data value
• Conditional expressions to make decisions
• Control structures to act on decisions
• Modules to make the algorithm manageable by abstraction (i.e., grouping related components)
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15. Fine! Then what is Programming?
Programming requires two skills:
Algorithmic thinking (hard!)
Knowledge of programming language syntax
The syntax is the easy part
Programming:
Start by developing a good algorithm
Then, convert into a language-specific syntax
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16. How to Learn Programming
We use pseudo-code to focus on learning algorithmic thinking
Not using a computer to compile and run your program forces you to mentally execute your program and debug it!
Too many programmers try to program by brute force and twiddling in an IDE. Wrong approach!
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17. Summary Programming starts with algorithm development
An algorithm is just a set of instructions
Abstraction is just the level of detail
A good algorithm exhibits precision, clarity, completeness, correctness, and simplicity.
An algorithm can be described using a natural language, pictures and diagrams, and pseudocode or a specific programming language.
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